Dear Doctor K: My doctor thinks I may have asthma. He wants to do
a pulmonary function test. What can I expect?

Dear Reader: Pulmonary function testing examines different
aspects of how your lungs function. During the test, you will
breathe in and out through a tube that is connected to various
machines. A test called spirometry measures how forcefully you can
inhale and exhale while taking as large a breath as possible. You
can skew the results by not trying hard.
A separate test will measure your lung volume: how much air your
lungs can hold, and how much air is left in your lungs when you
breathe out as much as you can. This may be done in one of two ways.
One way is to have you inhale a small amount of a specific gas (such
as helium).
You can also measure lung volume by sitting inside an airtight
cubicle. You breathe in and out through a pipe in the wall. Your
breathing will cause the air pressure inside the box to change. This
pressure change is measured and used to calculate the amount of air
you are breathing.
Your doctor will also want to measure how efficiently your lungs
deliver oxygen and other gases to your bloodstream. To measure this,
you breathe in a small quantity of carbon monoxide (too little to do
any harm). The amount of carbon dioxide you breathe back out is
measured. Your ability to absorb carbon monoxide is representative
of your ability to absorb other gases into your bloodstream.
Today, doctors can quite accurately measure the oxygen in your
blood with a simple device that clips to your finger.
What do doctors learn from pulmonary function testing? As in your
case, they can learn whether you have signs of asthma. They also can
determine if you have chronic obstructive pulmonary (or lung)
disease, known as COPD or COLD. This condition is seen most often in
long-term smokers.
You should hear back from your doctor within a week.
Write Dr. K at www.AskDoctorK.com or c/o Universal Uclick, 1130
Walnut, Kansas City, MO 64106